1. Field of the Invention
The present invention relates to disk recording media such as magneto-optical disks, and disk drive units that perform writing or reading operations adapted for the media.
2. Description of the Related Art
Recently, an increase in the density of recording media has been required, and various technologies for high-density writing and reading have been developed.
For example, magneto-optical (xe2x80x9cMOxe2x80x9d) disks have been used mainly for writing and reading computer data. As techniques for enabling high density recording on the magneto-optical disks, the magnetically induced super resolution (MSR) technique and the land/groove writing method have been developed.
In the land/groove writing method, both a land and a groove are used as recording tracks.
On a conventional magneto-optical disk, grooves are formed beforehand, and the grooves are used as recording tracks. By also using, as a recording track, the area or the land between one groove recording track and an adjacent groove recording track, the recording density of the disk can be greatly increased.
In the MSR technique, magnetic films having different temperature characteristics are used to read information recorded in a region smaller than the laser spot. Accordingly, from a medium (MSR medium) having recording regions composed of two magnetic films having different temperature characteristics, information written at a high density can be read without reducing the diameter of the laser spot.
The MSR reading method is described below with reference to FIG. 18.
The top portion (a) of FIG. 18 shows a recording track Dt of a magneto-optical disk on which write marks M are formed, and a laser spot SP impinging on the track Dt. The bottom portion (b) of FIG. 18 shows a partial cross section of the magneto-optical disk.
To obtain MSR effects, the magneto-optical disk must have, as shown in the bottom portion (b) of FIG. 18, a recording layer, an intermediate layer, and a reading layer that exhibit different magnetic characteristics depending on temperatures.
The reading layer functions as a mask for masking the write mark M from the laser spot SP when reading is performed.
The recording layer holds a written signal or information represented by the write mark M as a magnetization direction.
The intermediate layer controls the coupling between the reading layer and the recording layer.
By applying an external magnetic field to the reading layer when reading is performed, magnetization directions of the reading layer are aligned. This masks the recording layer (front masking). Here, by using the laser spot SP to heat the disk, in part of the laser spot SP which has an intermediate temperature of the heat distribution, the magnetized information on the recording layer, that is, the magnetization direction of the write mark M, is transferred to the reading layer. By observing the magnetization direction transferred to the reading layer, the write mark M, which is written at a high density, can be read, even if the laser spot SP has a large diameter.
In part of the laser spot SP which has a high temperature of the heat distribution, the reading layer and the recording layer are magnetically separated, and the reading layer functions to mask the recording layer from the external magnetic field (rear masking).
By using the above-described MSR technique, high-density writing and reading with a density at least double that of conventional techniques can be performed. This can greatly increase the recording capacity of the magneto-optical disk.
However, in achieving high density, the MSR technique and the land/groove writing method cause the following problems.
Although the MSR technique greatly increases the recording capacity of the magneto-optical disk, it cannot be applied to the entire surface of the magneto-optical disk.
For the magneto-optical disk, data units called xe2x80x9csectorsxe2x80x9d are employed as a basic data format, and data strings formed on the tracks of the disk consist of the sector units, which are sequential.
Each sector consists of a preformatted header (hereinafter also referred to simply as a xe2x80x9cheaderxe2x80x9d) in which preformat data is written by embossed pits, and a write/read area (hereinafter referred to as an xe2x80x9cMO areaxe2x80x9d for convenience of description) as a magneto-optical area in which data can be written or read, as shown in FIG. 19.
In the header, a sector address, etc., is written by embossed pits.
In the MO area, data including user data are written.
Accordingly, in the sectors of the magneto-optical disk, a recording film adapted for the MSR technique can be formed only in the MO area. The MSR technique cannot be applied to the header.
On the magneto-optical disk, at a predetermined position in an outer peripheral or inner portion, an area in which system information and write information are prewritten is preformatted. The MSR technique cannot be applied to this preformatted area.
In other words, in the preformatted area and the preformatted header of the sector, pre-recorded pits (hereinafter referred to as xe2x80x9cprepitsxe2x80x9d) must be formed at a conventional recording density because the MSR technique cannot be used.
As a result, the length of one byte is physically longer in the preformatted header than in the MO area. The area in the disk in which system information and write information are prewritten has greater redundancy.
In addition, a double-sided 5.2-gigabyte magneto-optical disk has a groove width of approximately 0.55 xcexcm when employing the land/groove writing method. On a track formed on a groove G, a preformatted header is provided for the start of each sector, as shown in the top portion (a) of FIG. 20.
In this configuration, a land L between one track (groove G) and an adjacent track (groove G) acts as a shield against crosstalk from a preformatted header on the adjacent track.
In the header, address information that has a single value is written twice as ID1 and ID2.
Referring to the intermediate portion (b) of FIG. 20, when the land/groove writing method is also considered which has an identical pitch between groove tracks G and which uses a land L as a recording track in addition to the groove tracks G, the land L has a preformatted header similar to that on the adjacent groove tracks G, and has no shield for the header. Therefore, generated crosstalk makes it very difficult to read sector-address information written in the header on the land L. This causes deterioration in writing/reading performance or seeking performance.
In a general technique for avoiding the deterioration in performance, as shown in the bottom portion (c) of FIG. 20, the preformatted headers on the land track L and the groove track G are not radially arranged but either of tracks is arranged to be shifted backward by one length in the track direction. This can prevent the crosstalk from affecting address information to be read.
However, this case causes large redundancy since the start of each sector must have an area which is double the header area.
When the redundancy caused by the preformatted header in the employment of the MSR technique, and the redundancy caused by crosstalk avoidance in the land/groove writing method are taken into consideration, at least 5 percent of the total recording capacity is wasted. In other words, simply employing the MSR technique and the land/groove writing method cannot achieve an effective increase in the recording capacity.
Accordingly, for enabling a large recording capacity, the redundancy caused by the preformatted header in the employment of the MSR technique, and the redundancy caused by crosstalk avoidance in the land/groove writing method must be reduced.
Accordingly, it is an object of the present invention to provide a disk recording medium the recording density of which is increased by an effective data arrangement in the header of each sector, using the MSR technique or the land/groove method, and a disk drive unit therefor.
To this end, according to an aspect of the present invention, the foregoing object is achieved through provision of a disk recording medium having recording tracks in the form of groove tracks and land tracks which each have sectors as data units. In the disk recording medium, each of the sectors includes a preformatted-data-recorded header area and a writing/reading area in which data is written or read, and the header area includes at least both a first address and a second address which have identical address numbers, and the first address and the second address are positioned to be reversely displaced from the center line of one groove track or one land track to the radial direction of the disk recording medium.
Preferably, one of the first address and the second address corresponds to a sector on one groove track, and the other one of the first address and the second address corresponds to a sector on one land track.
In the writing/reading area, a recording film for use in reading by the magnetically induced super resolution technique may be formed.
A plurality of zones may be radially formed on the disk recording medium, and only either of the first address and the second address may be positioned in a boundary area between adjacent zones.
In at least one zone, logically different addresses may be assigned to the groove tracks and the land tracks.
According to another aspect of the present invention, the foregoing object is achieved through provision of a disk drive unit for a disk recording medium which has recording tracks in the form of groove tracks and land tracks each having sectors as data units, and in which the sectors each include a preformatted-data-recorded header area and a writing/reading area in which data is written or read, and the header area includes at least both a first address and a second address which have identical address values, and the first address and the second address are positioned to be reversely displaced from the center line of one groove track or one land track to the radial direction of the disk recording medium. The disk drive unit includes a head unit for writing/reading information to/from the groove tracks and the land tracks, and a control unit for controlling the head unit to perform a writing operation or a reading operation based on a sector address on the groove track or a sector address on the land track which is determined using the address values read at the first address and the second address by the head unit.
Preferably, the disk drive unit further includes a servo unit for switching scanning modes of writing or reading by the head unit, which correspond to the scanning of the groove tracks and the scanning of the land tracks. The control unit determines, based on the scanning mode switched by the servo unit and the two address values at the first address and the second address, the sector address on the groove track or the sector address on the land track.
Preferably, the two address values are identical for one of the groove track and the land track, and have a predetermined differential value for the other one of the groove track and the land track.
The disk recording medium may have a plurality of zones that are radially formed, and when the head unit scans either the groove track or the land track, the control unit may specify one zone based on the difference between the two address values read at the first address and the second address.